Simplified Method Of Dynamic Full-scale Pile-soil Interaction In Liquefying Ground

Liquefaction is the main reason of earthquake-induced damage to the pile-supported bridge. The study on dynamic pile-soil interaction is the key point to solvethis problem in liquefying ground. Now most of the research work is based on the smallscale model test (shaking table test and centrifuge test) and the corresponding methodsof numerical simulation. Therefore, this paper developed the study on the numericalsimulation of full-scale bridge pile foundation in liquefying ground, which is based onthe modeling approach to three-dimensional finite element model that is validated bythe shaking table test, and using the dynamic calculation parameters of Nevada sandwhich calibrating by the centrifuge test in VELACS. Using this numerical model, themain factors affecting p-y curves were studied, a formula for the p-y curves ofliquefying sand was built and a simplified method for analysis of dynamic pile-soilinteraction in liquefying ground was developed. The main obtained research andunderstandings are as follows:Firstly, a three-dimensional finite element model is established for shaking tabletest of dynamic soil-pile interaction. Some governing equations of u-p formulation areused in this model to describe the dynamic properties of saturated sand. Choosingplastic multi-yield surface constitutive model to describe the dynamic properties ofsaturated sand and using the beam-column element to simulate the pile in this model.The correctness of the numerical model technique approach was validated through theshaking table test. A three-dimensional finite element model of dynamic full-scalebridge pile foundation in liquefying ground is built which is based on the abovemodeling approach. In this numerical model, choosing the Nevada sand as the soil mass,the dynamic calculation parameters of the Nevada sand calibrating by the centrifuge test,and then analyzes the dynamic characteristics of the numerical model. The results showthat acceleration amplitude of pile and soil are reduction after soil liquefaction.Secondly, a series of numerical simulation from3D finite element analysismethod were conducted under a series of sine waves to investigate the effect ofacceleration amplitude of cyclic loading, permeability of sand, friction angle of sandand pile diameter on dynamic p-y curves in liquefying ground. Dynamic p-y curves ofmedium-dense sand was obtained. It is observed that the different values of accelerationamplitudes, pile diameters and soil permeability has significant influences on dynamicp-y curve; The area of hysteresis loop increases obviously as the soil is liquefied. Andthe shallow soil layer will have a large plastic deformation because of soil liquefaction.Thirdly, the backbone curve of dynamic p-y curves was proposed by thecharacteristics of dynamic p-y curves based on the soil stress-strain backbone curve. Besides, by amending the p-y curve formula of saturated sand from the API, asimplified expression of the backbone curve of dynamic p-y curves in liquefying groundtaking pore pressure ratio as a control variable was established.Finally, combining spring element, plasticity element and gap element in seriesfor simulating the basic characteristics of dynamic pile-soil interaction, and blending inthe newly created simplify expressions of p-y curves, a simplified dynamic full-scalepile-soil interaction model and analysis method were established. What’s more, thesimplified method was verified by the results of finite element method.